This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The mitotic spindle assembly checkpoint (SAC) is the only known checkpoint in mitosis. The SAC is composed of complex multi-signal transduction pathways that promote the proper segregation of chromosomes during cell division. As such, defects in the SAC result in chromosome instability (CIN), a hallmark of cancer. Of clinical importance, apoptosis caused by mitotic catastrophe depends on the activation of SAC. However, our knowledge of SAC signaling is far from complete, and the functional cross-talk between SAC activation and the induction of mitotic apoptosis is poorly understood. This makes it difficult to explain the mechanism by which cancer cells respond or become refractory to anti-mitotic drugs, e.g. taxol, that induced spindle-damage or mitotic catastrophe. Therefore, it is highly important to understand both the molecular mechanism by which SAC (i) controls proper chromosome segregation to maintain chromosome stability during cell division and (ii) elicits an apoptotic response in mitosis to anti-mitotic cancer therapeutic drugs. Specific Aims 1. Determine the molecular mechanisms by which the SAC-machinery controls SAC signaling and SAC-mediated mitotic cell death. a. Identify the protein components in the SAC machinery that are required for SAC-dependent mitotic cell death. b. Identify the signaling proteins that interact with the protein components in the SAC machinery that are required for SAC-dependent mitotic cell death. c. Identify the mechanism by which these signaling proteins control SAC signaling and elicit mitotic cell death.